1. Field of the Invention
The present invention relates to a calibration device for apparatus filling a gas such as hydrogen gas, and more particularly to a calibration device capable of precisely measuring quantity of a gas such as hydrogen gas filled at high pressure.
2. Description of the Related Art
Gasoline meters installed in filling stations are obliged to take flow rate verification every seven years to maintain fair business dealing, and it is requested that instrumental error of the flow meter is within ±0.5 percent. To such request, the applicant proposes a gasoline meter with inspection mechanism of flow meters in Japanese Patent Publication No. Heisei 07-33197.
In recent years, as a countermeasure for environmental issue, fuel-cell automobiles using hydrogen as fuel have been developed, accordingly hydrogen filling apparatus and calibration devices for the hydrogen filling apparatus have been investigated.
Here in the filling of the hydrogen, high pressure filling is adopted to shorten the filling time, but temperature of the gas increases in association with the high pressure filling, and fuel tanks of fuel-cell vehicles become high in temperature, which may cause breakage of the fuel tanks. In order to prevent the possibility, hydrogen is filled while being cooled at −40° C. with a cooling device.
However, when hydrogen is filled into a calibration device of a hydrogen filling apparatus while being cooled at −40° C., temperatures of a receptacle, a filling gas supply pipe, a filling vessel and other parts become lower than ambient temperature, so that dew condenses on the equipment. When the dew evaporates, weight of overall calibration device changes, resulting in a problem that precise calibration becomes impossible.
In addition, when hydrogen gas is released form the filling vessel of the calibration device, temperature of the filling vessel becomes low due to adiabatic expansion phenomenon to produce water droplets through dew condensation. Then, when several calibrations are performed, due condensations and evaporations repeatedly occur on the large surfaces of the filling vessel, so that weight changes of the calibration device are remarkable, resulting in impossibility of precise measurement.
The contents of Japanese Patent Publication No. Heisei 07-33197 is incorporated herein by reference in its entirety.